A toggle-type mold clamping apparatus is widely used in a molding apparatus, such as an injection molding machine. In a toggle-type mold clamping apparatus, a toggle link mechanism that generates a mold opening/closing force and a mold clamping force is provided between a pressure-receiving platen and a movable platen.
Among various molding methods using an injection molding machine, a foam molding method has recently attracted attention. The foam molding method can produce a molded resin product containing a myriad of air bubbles. Thus, the foam molding method can produce a light-weight molded product and, in addition, can impart heat insulating properties, sound absorbing properties, etc, to the molded product.
In foam molding, after clamping a mold, a molten resin containing a foaming agent is filled into a cavity of the mold. After a surface layer of the molten resin becomes solidified into a skin layer, it is necessary to slightly open the mold (“core-back” operation) and increase the volume of the cavity in order to foam the molten resin. In foam molding, the thickness and the foaming state of a molded product are determined by the degree of opening of the mold upon the slightly mold-opening operation. Therefore, the stopping accuracy of a movable platen upon the slightly mold-opening operation is a very important factor for ensuring the quality of the molded product.
The stopping accuracy of a movable platen upon the slightly mold-opening operation is of significance especially for a molding apparatus provided with a toggle-type mold clamping apparatus. This is because in a toggle-type mold clamping apparatus, a slight gap exists between a pin and a link connecting portion that connects links of a toggle link mechanism, and an error caused by the gap will decrease the stopping accuracy of a movable platen.
In order to enhance the stopping accuracy of a movable platen upon the slightly mold-opening operation, various improvements have been made in a toggle-type mold clamping apparatus.
For example, Japanese Patent Laid-Open Publication No. 2006-334793 has proposed a toggle-type mold clamping apparatus provided with a cavity expansion mechanism, disposed near a mold between a fixed platen and a movable platen, for pushing and moving the movable platen in conjunction with expansion of a cavity of the mold.
Japanese Patent Laid-Open Publication No. 2011-31535 describes a toggle-type mold clamping apparatus including a rotating platen disposed between a fixed platen and a movable platen. A mold having two types of product cavities of different shapes is mounted to the rotating platen. When opening the mold upon foam molding, the movable platen is pushed and moved in the mold opening direction by means of a drive mechanism which moves the rotating platen in mold opening/closing directions.
Japanese Patent Laid-Open Publication No. 2008-110498 discloses a toggle-type mold clamping apparatus including a movable platen consisting of a first movable platen to which a toggle mechanism is axially mounted, and a second movable platen to which a movable mold is mounted. A hydraulic cylinder and a position sensor are disposed between the first movable platen and the second movable platen.